Inkjet printing has been widely spread as a printer for office use and domestic use, in a trend of progressing digitalization of information, and recently a lot of trials are promoted to expand applications thereof further to commercial printing, textile printing, etc. Regarding to a coloring material to be used for the ink, together with spreading in use of the inkjet printing, various kinds of coloring materials have come into practical use covering from the conventional water-soluble dyes such as acidic dye or direct dye and the like to water-insoluble coloring materials such as disperse dye and pigment and the like corresponding to applications thereof.
Meanwhile, disperse dye has been widely used in the industrial dyeing of hydrophobic fibers such as polyesters, where a water-insoluble dye is used for dyeing by dispersing in a dyeing bath or a coloring paste. A dye penetrates and diffuses into a fiber under a high temperature condition, and fixed by means of hydrogen bond, intermolecular force, etc. between the fiber and the dye. A dye inferior in dispersibility, in particular, at a high temperature tends to aggregate in a dyeing bath at a high temperature to form a speck on a fiber. For this reason, conventionally a dispersing agent superior in high temperature dispersibility, for example, an anionic dispersing agent such as formaldehyde condensates of lignin sulfonic acid, formaldehyde condensates of alkylnaphthalene sulfonic acid and formaldehyde condensates of creosote oil sulfonic acid had been mainly used.
Further, inkjet printing to polyester fiber using a disperse dye has been also carried out (see, for example, Non-Patent Literature 1 and Non-Patent Literature 2), and mainly, a direct printing method where a dye ink is given (printed) to a fiber followed by fixing of the dye by heat treatment such as steaming, and a thermal transfer printing method where after a dye ink is given (printed) to an intermediate recording medium (a special transfer paper) the dye is transferred by sublimation from the intermediate recording medium to a fiber, have been practically utilized. In order to disperse the disperse dye inks used in these printing methods, an anionic dispersing agent, which has been conventionally used for industrial dyeing, is utilized (see, for example, Patent Literature 1 and Patent Literature 2). In addition, Patent Literature 3 discloses use of an ethylene oxide adduct of linear alkyl as a dispersing agent.
However, none of these compounds satisfied settling stability and shelf life stability of an aqueous dispersion and an ink composition, as well as jetting stability of an ink composition from printer.
Further, Patent Literature 4 exemplifies polyoxyethylene phytosterol together with polyoxyethylene alkyl ether, etc. as one of nonionic surfactants which are used as a surface tension regulator to be used for an ink for inkjet recording, however, specific example of use thereof, etc. has not been disclosed at all.
Patent Literature 1: JP-A-H9-291235
Patent Literature 2: JP-A-H8-333531
Patent Literature 3: JP-A-2003-246954
Patent Literature 4: JP-A-2001-329196
Non-Patent Literature 1: Journal of the Imaging Society of Japan, Vol. 41, No. 2, p. 68-74 (2002)
Non-Patent Literature 2: Senshoku Keizai Shimbun, 28th Jan. 2004, P. 18-21.